/Engine/Plugins/Online/OnlineSubsystem/Source/Public/Interfaces/OnlineMessageInterface.h
Get the cached list of message headers for a user. Cache is populated by calling EnumerateMessages
true if cached entry was found
bool GetMessageHeaders ( int32 LocalUserNum, [TArray](API\Runtime\Core\Containers\TArray)< [TSharedRef](API\Runtime\Core\Templates\TSharedRef)< class [FOnlineMessageHeader](API\Plugins\OnlineSubsystem\Interfaces\FOnlineMessageHeader) > > & OutHeaders )